Organic electroluminescent element, display device and illuminating device

ABSTRACT

Disclosed is an organic electroluminescent element having high luminous efficiency and long life. Also disclosed are a display device and an illuminating device respectively using such an organic electroluminescent element. Specifically disclosed is an organic electroluminescent element comprising an electrode and at least one or more organic layers on a substrate. This organic electroluminescent element is characterized in that at least one of the organic layers is a light-emitting layer containing a phosphorescent compound and a host compound, the phosphorescent compound has a HOMO of −5.15 to −3.50 eV and a LUMO of from −1.25 to +1.00 eV, and the host compound has a 0-0 band of the phosphorescence spectrum at not more than 460 nm and a glass transition temperature of not less than 60° C.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/293,736, filed on Sep. 19, 2008, now U.S. Pat.No. 8,920,942, the entire contents of which are incorporated herein byreference and priority to which is hereby claimed. application Ser. No.12/293,736 is the U.S. National stage of application No.PCT/JP2007/055608, filed Mar. 20, 2007, the entire contents of which areincorporated herein by reference. Priority under 35 U.S.C. §119(a) and35 U.S.C. §365(b) is hereby claimed from Japanese Application No.2006-079918, filed Mar. 23, 2006, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an organic electroluminescent element,a display device and a lighting device.

BACKGROUND OF ART

Conventionally, an emission type electronic display device includes anelectroluminescence display (hereinafter, referred to as an ELD). Aconstituent element of ELD includes such as an inorganicelectroluminescent element and an organic electroluminescent element(hereinafter, referred to as an organic EL element). An inorganicelectroluminescent element has been utilized as a flat light source,however, requires a high voltage of alternating current to operate anemission element.

On the other hand, an organic electroluminescent element is an elementprovided with a constitution comprising an emission layer containing aemitting substance being sandwiched with a cathode and an anode, and anexciton is generated by an electron and a positive hole being injectedinto the emission layer to be recombined, resulting emission utilizinglight release (fluorescence phosphorescence) at the time of deactivationof said exciton; the emission is possible at a voltage of approximatelya few to a few tens volts, and an organic electroluminescent element isattracting attention with respect to such as superior viewing angle andhigh visual recognition due to a self-emission type as well as spacesaving and portability due to a completely solid element of a thin layertype.

In an organic electroluminescence in view of the future practicalapplication, desired has been development of an organic EL element whichefficiently emits at a high luminance with a low electric consumption.Examples of such technologies are a slight amount of a fluorescentsubstance doped in a stilbene derivative, distyrylarylene derivative ora tristyrylarylene derivative, to achieve improved emission luminanceand a prolonged lifetime of an element (for example, refer to PatentDocument No. 1). Further, there are known such as an element having anorganic emission layer comprising a 8-hydroxyquinoline aluminum complexas a host compound which is doped with a slight amount of a fluorescentsubstance (for example, refer to Patent Document No. 2) and an elementhaving an organic emission layer comprising a 8-hydroxyquinolinealuminum complex as a host compound which is doped with quinacridonetype dye (for example, refer to Patent Document No. 3).

Regarding to the technologies disclosed in the above-described PatentDocuments, when emission from an excited singlet is utilized, since ageneration ratio of a singlet exciton to a triplet exciton is 1/3, thatis, a generation probability of an emitting exciton species is 25% and alight taking out efficiency is approximately 20%, the limit of a quantumefficiency (next) of taking out is said to be 5%.

However, since an organic EL element which utilizes phosphorescence froman excited triplet has been reported from Princeton University (forexample, refer to Non Patent Document 1), researches on materialsexhibiting phosphorescence at room temperature have come to be active(for example, refer to Non Patent Document 2). Since the upper limit ofinternal quantum efficiency becomes 100% by utilization of an excitedtriplet, which is principally 4 times of the case of an excited singlet,it may be possible to achieve almost the same ability as a cooledcathode ray tube to attract attention also for an illuminationapplication. As a dopant used for an organic electroluminescent elementemploying phosphorescence, many compounds mainly belonging to iridiumcomplexes have been investigated (for example, refer to Non PatentDocument No. 3).

An example is tris(2-phenylpyridine)iridium (refer to Non PatentDocument No. 2). In addition to that, there have been studied to useL₂Ir(acac) such as (ppy)₂Ir(acac) as a dopant (for example, refer to NonPatent Document No. 4). Also there have been studied to use compoundssuch as tris(2-(p-tolyl)pyridine)iridium (Ir(ptpy)₃) andtris(benzo[h]quinoline)iridium (Ir(bzq)₃), Ir(bzq)₂CIP(Bu)₃ (forexample, refer to Non Patent Document No. 5). Also known areinvestigations on iridium complexes having phenyl pyrazole as a ligand(refer to Non Patent Documents No. 4).

A FIrpic, which is a typical phosphorescent blue dopant, has achieved ashortening of emission wavelength with a fluorine-substitutedphenylpyridine and a picolinic acid being employed as a major ligand andan auxiliary ligand respectively. As an auxiliary ligand, other than thepicolinic acid, a pirazabole type ligand has been known to shorten anemission wavelength by being introduced into the dopant. (for example,refer to Patent Document 1 and Non-Patent Documents 1 and 2). Theaforesaid dopants, in combination with carbazol derivatives ortriarylsilanes as a host compound, have realized high efficientelements, but on the other hand, have significantly degraded emissionlife of the elements. Then, improvement to overcome the trade-offrelationship has been demanded.

Any of the above-described blue dopants are such types of compounds thatthe dopant materials have a low level of the highest occupied molecularorbital (hereinafter abbreviated as “HOMO”) and the lowest unoccupiedmolecular orbital (hereinafter abbreviated as “LUMO”). HOMO and LUMOlevels of the above dopants are lower by about 1 eV compared to those ofa Ir(ppy)₃, which is a typical phosphorescent green dopant. As a bluedopant, compounds having low HOMO and LUMO levels have been known, butonly a few compounds having high HOMO and LUMO levels have beenreported. Recently, blue dopants having high HOMO-LUMO levels werereported (refer to Patent Documents 5 and 6), but these dopants areinsufficient with regard to efficiency and life, therefore theachievements of higher efficiency and longer life are the issues.

-   Patent Document 1: Japanese Patent Registration No. 3093796-   Patent Document 2: Unexamined Japanese Patent Application    Publication (hereinafter referred to as JP-A) No. 63-264692-   Patent Document 3: JP-A No. 3-255190-   Patent Document 4: WO 04/085450-   Patent Document 5: U.S. Patent Registration No. 2004/0048101-   Patent Document 6: WO 04/085450-   Non-Patent Document 1: M. A. Baldo et al., Nature, Vol. 395, pages    151-154 (1998)-   Non-Patent Document 2: M. A. Baldo et al., Nature, Vol. 403, No. 17,    pages 750-753 (2000)-   Non-Patent Document 3: S. Lamansky et al., J. Am. Chem. Soc., Vol.    123, page 4304 (2001)-   Non-Patent Document 4: M. E. Tompson et al., The 10th International    Workshop on Inorganic and Organic Electroluminescence (EL'00,    Hamamatsu)-   Non-Patent Document 5: Moon-Jae Youn. Og, Tetsuo Tsutsui et al., The    10th International Workshop on Inorganic and Organic    Electroluminescence (EL'00, Hamamatsu)

DISCLOSURE OF THE INVENTION Issues to be Solved by the Invention

The object of the present invention is to provide an organicelectroluminescent element exhibiting high light emission efficiency andlong life, and a lighting device and a display device both of whichemploy the aforesaid element.

Measures to Solve the Issue

The above issues have been achieved by the following constitutions.

1. An organic electroluminescent element having electrodes and at leastone organic layer on a substrate, wherein at least one of the aforesaidorganic layers is a light-emitting layer incorporating a phosphorescentcompound and a host compound; the aforesaid phosphorescent compound hasa HOMO of −5.15 to −3.50 eV and a LUMO of −1.25 to 1.00 eV; and theaforesaid host compound has the phosphorescence 0-0 band of not morethan 460 nm, and the glass transition point of not less than 60° C.

2. The organic electroluminescent element of the Item 1, wherein theabove-described phosphorescent compound has a HOMO of −4.80 to −3.50 eV,and a LUMO of −0.80 to 1.00 eV.

3. An organic electroluminescent element of Items 1 or 2, wherein theabove-described phosphorescent compound is represented by Formula (A)below.

(wherein R₁ represents a substituent; Z represents a non-metal atomgroup necessary to form a 5 to 7-membered ring; n1 represents an integerof 0 to 5; each B₁ to B₅ independently represents a carbon atom, anitrogen atom, an oxygen atom or a sulfur atom, provided that one ofwhich represents a nitrogen atom; M₁ represents a metal of Group 8 to 10of the Periodic Table of the Elements; each X₁ and X₂ independentlyrepresent a carbon atom, a nitrogen atom, or an oxygen atom; L₁,together with X₁ and X₂, represents a group of atoms to form a bidentateligand; and m1 is an integer of 1 to 3, and m2 is an integer of 0 to 2,provided that a sum of m1 and m2 is 2 or 3.)

4. The organic electroluminescent element of any one of the Items 1 to3, wherein m2 is 0 in the phosphorescent compound represented by theabove-described Formula (A).

5. The organic electroluminescent element of any one of the Items 1 to4, wherein a nitrogen-containing heterocycle formed by B₁ to B₅ is animidazole ring in the phosphorescent compound represented by theabove-described Formula (A).

6. The organic electroluminescent element of any one of the Items of 1to 5, wherein the above-described Formula (A) is represented by Formula(B) below.

(wherein R₁, R₂, and R₃ represents a substituent; Z represents anon-metal atom group necessary to form a 5 to 7-membered ring; n1represents an integer of 0 to 5; M₁ represents a metal of Group 8 to 10of the Periodic Table of the Elements; each X₁ and X₂ independentlyrepresents a carbon atom, a nitrogen atom, or an oxygen atom; L₁,together with X₁ and X₂, represents a group of atoms to form a bidentateligand; and m1 is an integer of 1 to 3, and m2 is an integer of 0 to 2,provided that a sum of m1 and m2 is 2 or 3.)

7. The organic electroluminescent element of the Item 6, wherein, in theabove-described Formula (B), a substituent represented by R₂ isrepresented by Formula (C) below.

(wherein R₄ represents a substituent having a steric parameter value (anEs value) of not more than −0.5, R₅ represents a substituent, and n5represents an integer of 0 to 4. The asterisk “*” in the Formulaindicates a bonding position.)

8. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (1) below.

(wherein R_(1a) represents a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group; each R₁ and R₂ independentlyrepresent a hydrogen atom or a substituent; and each n1 and n2represents an integer of 0 to 4.)

9. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (2) below.

(wherein each R₁ and R₂ independently represents a hydrogen atom or asubstituent; R₃ represents a substituent; L₁ represents a bivalentlinking group; n1 and n2 represents an integer of 0 to 4; and m1represents an integer of 0 to 5.)

10. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (3) below.

(wherein each R₁, R₂, and R₄ independently represents a hydrogen atom ora substituent; L₃ represents a bivalent linking group; Ar₁ represents anaromatic group or a heterocyclic group; each n1 to n3 represents aninteger of 0 to 4; and m3 represents an integer of 0 or 1.)

11. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (4) below.

(wherein R_(1a) represents a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group; each R₁ and R₂ represents asubstituent; L₃ represents a bivalent linking group; Ar₁ represents anaromatic group or a heterocyclic group; each n1 and n2 represents aninteger of 0 to 4; and m3 represents an integer of 0 or 1.)

12. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (5) below.

(wherein R_(1a) represents a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group; each R₁ and R₂ independentlyrepresents a hydrogen atom or a substituent; L₃ represents a bivalentlinking group; Ar₁ represents an aromatic group or a heterocyclic group;n1 represents an integer of 0 to 4; n2 represents an integer of 0 to 3;and m3 represents an integer of 0 or 1.)

13. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (6) below.

(wherein R_(1a) represents a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group; each R₁, R₂ and R₅independently represents a hydrogen atom or a substituent; L₄ representsa bivalent linking group; Ar₁ represents an aromatic group or aheterocyclic group; each n1 and n4 represents an integer of 0 to 4; n2represents an integer of 0 to 3; and m4 represents an integer of 0 or1.)

14. The organic electroluminescent element of any one of the Items of 1to 7, wherein the above-described host compound is represented byFormula (7) below.

(wherein each R₁, R₂, and Ra independently represent a hydrogen atom ora substituent; each n1, n2 and na represents an integer of 0 to 4; and Xrepresents NRb, S, or O.)

15. The organic electroluminescent element of any one of the Items of 8to 13, wherein Ar₁ in Formulae (3) to (6) is a carbazolyl group.

16. The organic electroluminescent element of any one of the Items of 1to 15, wherein the above-described host compound exhibits the glasstransition point of not less than 90° C.

17. The organic electroluminescent element of any one of the Items of 1to 15, wherein the above-described host compound exhibits the glasstransition point of not less than 130° C.

18. The organic electroluminescent element of any one of the Items of 1to 15, wherein the above-described host compound exhibits the glasstransition point of not less than 160° C.

19. The organic electroluminescent element of any one of the Items of 1to 18, wherein the aforesaid organic electroluminescent element has anelectron blocking layer.

20. The organic electroluminescent element of any one of the Items of 1to 19, wherein the aforesaid organic electroluminescent element emitswhite light.

21. The display device, wherein the aforesaid device is provided withthe organic electroluminescent element of any one of the Items of 1 to20.

22. The lighting device, wherein the aforesaid device is provided withthe organic electroluminescent element of any one of the Items of 1 to20.

23. The display device, wherein the aforesaid device is provided withthe lighting device described in Item 22 and a liquid crystal element asa display means.

Effects of the Invention

According to the present invention, an organic electroluminescentelement having high light emission efficiency and a long life, and alighting device and a display device both of which employ the aforesaidelement, can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing to show an example of a display deviceconstituted of an organic EL element.

FIG. 2 is a schematic drawing of display section A.

FIG. 3 is an equivalent circuit diagram of an image pixel.

FIG. 4 is a schematic drawing of a full color display device accordingto a passive matrix mode.

FIG. 5 is a schematic drawing of a lighting device.

FIG. 6 is a schematic cross-sectional view of a lighting device.

DESCRIPTION OF SYMBOLS

-   -   1 display    -   3 pixel    -   5 scanning line    -   6 data line    -   7 electrical power line    -   10 organic EL element    -   11 switching transistor    -   12 operating transistor    -   13 capacitor    -   A display section    -   B control section    -   107 glass substrate having a transparent electrode    -   106 organic EL layer    -   105 cathode    -   102 glass cover    -   108 nitrogen gas    -   109 desiccant

MOST PREFERRED EMBODIMENTS TO CARRY OUT THE INVENTION

As a result of close examination, in view of the foregoing, by theinventors of the present invention, an organic electroluminescentelement having high light emission efficiency and long emission life wasprovided by employing any one of constituents of Items 1 to 23 in theorganic electroluminescent element of the present invention. Further, adisplay device and a lighting device both of which have high brightnessand long life were provided by employing the organic electroluminescentelement which exhibits the above-described properties.

The present invention will be described in details as below.

Phosphorescent Compound

Phosphorescent compounds in the emitting layer of the present inventioneach has a HOMO level of −5.15 to −3.50 eV and a LUMO level of −1.25 to+1.00 eV. More preferably, it has a HOMO level of −4.80 to −3.50 eV anda LUMO level of −0.80 to +1.00 eV.

In the present invention, the values of HOMO and LUMO levels denote thevalues obtained by calculations using Gaussian 98 (Gaussian 98, RevisionA. 11. 4, M. J. Frisch, et al, Gaussian, Inc., Pittsburg Pa., 2002),which is software for a molecular orbital calculation, and produced byGaussian Inc. The values of HOMO and LUMO levels of the host compound ofthe present invention are defined as values (a converted value in eVunit) calculated via structure optimization employing B3LYP/6-31G* as akey word. And the values of HOMO and LUMO levels of the phosphorescentcompound of the present invention are defined as values (a convertedvalue in eV unit) calculated via structure optimization employingB3LYP/LanL2DZ as a key word. The reason for the calculated value beingconsidered to be valid is that the calculated value obtained by theabove method is in good agreement with the experimental one.

<Phosphorescent Compound Represented by Formula (A)>

In the present invention, phosphorescent compounds represented byFormula (A) are preferable as the aforesaid phosphorescent compounds.

In Formula (A) for a phosphorescent compound in the present invention, asubstituent represented by R₁ are as follows. Examples of such asubstituent include an alkyl group (for example, a methyl group, anethyl group, a propyl group, an isopropyl group, a tert-butyl group, apentyl group, a hexyl group, an octyl group, a dodecyl group, a tridecylgroup, a tetradecyl group, and a pentadecyl group), a cycloalkyl group(for example, a cyclopentyl group and a cyclohexyl group), an alkenylgroup (for example, a vinyl group and an allyl group), an alkynyl group(for example, an ethynyl group and a propargyl group), an aromatichydrocarbon ring group (also called an aromatic carbon ring group or anaryl group such as a phenyl group, a p-chlorophenyl group, a mesitylgroup, a tolyl group, a xylyl group, a naphthyl group, an anthryl group,an azulenyl group, an acenaphthenyl group, fluorenyl group, aphenanthryl group, an indenyl group, a pyrenyl group, or a biphenylgroup), an aromatic heterocyclic group (for example, a pyridyl group, apyrimidinyl group, a furyl group, a pyrrolyl group, an imidazolyl group,a benzimidazolyl group, a pyrazolyl group, a piradinyl group, atriazolyl group (for example, a 1,2,4-triazole-1-yl group and a1,2,3-triazole-1-yl group), an oxazolyl group, a benzoxazolyl group, athiazolyl group, an isooxazolyl group, an isothiazolyl group, afurazanyl group, a thienyl group, a quinolyl group, a benzofuryl group,a dibenzofuryl group, a benzothienyl group, a dibenzothienyl group, anindolyl group, a carbazolyl group, a carbolynyl group, a diazacarbazoylgroup (which shows that one of the carbon atoms which constitute acarboline ring of the above carbolinyl group is replaced with a nitrogenatom), a quinoxythalinyl group, a pyridazinyl group, a triazinyl group,a quinazolinyl group, a phthalazinyl group), a heterocyclic group (forexample, a pyrrolidinyl group, an imidazolidyl group, a morpholyl group,and an oxazolidyl group), an alkoxy group (for example, a methoxy group,an ethoxy group, a propyloxy group, a pentyloxy group, a hexyloxy group,an octyloxy group, and a dodecyloxy group), a cycloalkoxy group (forexample, a cyclopentyloxy group and a cyclohexyloxy group), an aryloxygroup (for example, a phenoxy group and a naphthyloxy group), analkylthio group (for example, a methylthio gropup, an ethylthio group, apropylthio group, a pentylthio group, a hexylthio group, an octylthiogroup, and a dodecylthio group), a cycloalkylthio group (for example, acyclopentylthio group and a cyclohexylthio group), an arylthio group(for example, a phenylthio group and a naphthylthio group), analkoxycarbonyl group (for example, a methyloxycarbonyl group, anethyloxycarbonyl group, a butyloxycarbonyl group, an octyloxycarbonylgroup, and a dodecyloxycarbonyl group), an aryloxycarbonyl group (forexample, a phenyloxycarbonyl group and a naphthyloxycarbonyl group), asulfamoyl group (for example, an aminosulfonyl group, amethylaminosulfonyl group, a dimethylaminosulfonyl group, abutylaminosulfonyl group, a hexylaminosulfonyl group, acyclohexylaminosulfonyl group, an octylaminosulfonyl group, adodecylaminosulfonyl group, a phenylaminosulfonyl group, anaphthylaminosulfonyl group, and a 2-pyridylaminosulfonyl group), anacyl group (for example, an acetyl group, an ethylcarbonyl group, apropylcarbonyl group, a pentylcarbonyl group, a cyclohexylcarbonylgroup, an octylcarbonyl group, a 2-ethylhexylcarbonyl group, adodecylcarbonyl group, a phenylcarbonyl group, a naphthylcarbonyl group,a pyridylcarbonyl group), an acyloxy group (for example, an acetyloxygroup, an ethylcarbonyloxy group, a butylcarbonyloxy group, anoctylcarbonyloxy group, a dodecylcarbonyloxy group, and aphenylcarbonyloxy group), an amido group (for example, amethylcarbonylamino group, an ethylcarbonylamino group, adimethylcarbonylamino group, a propylcarbonylamino group, apentylcarbonylamino group, a cyclohexylcarbonylamino group, a2-ethylhexylcarbonylamino group, an octylcarbonylamino group, adodecylcarbonylamino group, a phenylcarbonylamino group, and anaphthylcarbonylamino group), a carbamoyl group (for example, anaminocarbonyl group, a methylaminocarbonyl group, adimethylaminocarbonyl group, a propylaminocarbonyl group, apentylaminocarbonyl group, a cyclohexylaminocarbonyl group, anoctylaminocarbonyl group, a 2-ethylhexylaminocarbonyl group, adodecylaminocarbonyl group, a phenylaminocarbonyl group, anaphthylaminocarbonyl group, and a 2-pyridylaminocarbonyl group), anureido group (for example, a methylureido group, an ethylureido group, apentylureido group, a cyclohexylureido group, an octylureido group, adodecylureido group, a phenylureido group, a naphthylureido group, and a2-pyridylaminoureido group), a sulfinyl group (for example, amethylsulfinyl group, an ethylsulfinyl group, a butylsulfinyl group, acyclohexylsulfinyl group, a 2-ethylhexylsulfinyl group, adocecylsulfinyl group, a phenylsulfinyl group, a naphthylsulfinyl group,and a 2-pyridylsulfinyl group), an alkylsulfonyl group (for example, amethylsulfonyl group, an ethylsulfonyl group, a butylsulfinyl group, acyclohexylsulfonyl group, a 2-ethylhexylsulfonyl group, and adodecylsulfonyl group), an arylsulfonyl group or a heteroarylsulfonylgroup (for example, a phenylsulfonyl group, a naphthylsulfonyl group,and a 2-pyridylsulfonyl group), an amino group (for example, an aminogroup, an ethylamino group, a dimethylamino group, a butylamino group, acyclopentylamino group, a 2-ethylhexylamino group, a dodecylamino group,an anilino group, a cyclopentylamino group, a 2-ethylhexylamino group, adodecylamino group, an anilino group, a naphthylamino group, and a2-pyridylamino group), a halogen atom (for example, a fluorine atom, achlorine atom, and a bromine atom), a fluorinated hydrocarbon group (forexample, a fluoromethyl group, a trifluoromethyl group, apentafluoroethyl group, and a pentafluorophenyl group), a cyano group, anitro group, a hydroxyl group, a mercapto group, and a silyl group (forexample, a trimethylsilyl group, a triisopropylsilyl group, atriphenylsilyl group, and a phenyldiethylsilyl group).

Of these substituents, an alkyl group and an aryl group are preferred.

Z represents a non-metal atom group necessary to form a 5 to 7-memberedring. Examples of a 5 to 7-membered ring formed by Z include a benzenering, a naphthalene ring, a pyridine ring, a pyrimidine ring, a pyrrolering, a thiophene ring, a pyrazole ring, an imidazole ring, an oxazolering, and thiazole ring, of which a benzene ring is preferred.

Each of B₁ to B₅ independently represents a carbon atom, a nitrogenatom, an oxygen atom, or a sulfur atom, provided that at least one of B₁to B₅ represent nitrogen. As an aromatic nitrogen-containing heterocycleformed of these five atoms, a monocycle is preferred. Examples thereofinclude a pyrrole ring, a pyrazole ring, an imidazole ring, a triazolering, a tetrazole ring, an oxazole ring, an isooxazole ring, a thiazolering, an isothiazole ring, an oxadiazole ring, and a thiadiazole ring.Of these, a pyrazole ring and an imidazole ring are preferred, and animidazole ring is more preferred. The above rings may be furthersubstituted with the above-described substituent. The preferablesubstituents are an alkyl group and an aryl group, and more preferableare a substituted aryl group and a non-substituted aryl group.

L₁, together with X₁ and X₂, represents an atom group necessary to forma bidentate ligand. Specific examples of the bidentate ligand,represented by X₁-L₁-X₂, include substituted or non-substitutedphenylpyridine, phenylpyrazole, phenylimidazole, phenyltriazole,phenyltetrazole, pyrazabole, picolinic acid, and acetylacetone.

The above groups may be further substituted with the above-describedsubstituent.

m1 represents an integer of 1 to 3, and m2 represents an integer of 0 to2, provided that a sum of m1 and m2 is 2 or 3, of which m2 is preferably0.

As a metal represented by M₁, a transition metal element (also simplyreferred to as a transition metal) of Group 8 to 10 of the PeriodicTable of the Elements is employed. Of these, iridium and platinum arepreferred, and iridium is more preferred.

The phosphorescent compound, represented by Formula (1) of the presentinvention, may or may not have a polymerizable group or a reactivegroup.

Further, the nitrogen-containing heterocycle in the above-describedFormula (1) formed by B₁ to B₅ is preferably an imidazole ring.

In case that the nitrogen-containing heterocycle formed by B₁ to B₅ isthe imidazole ring, the above-described Formula (A) is more preferablyrepresented by the above-described Formula (B).

In Formula (3), R₁, R₂, and R₃ represent a substituent; Z represents anon-metal atom group necessary to form a 5 to 7-membered ring; n1represents a integer of 0 to 5; M₁ represents a metal of Group 8 to 10of the Periodic Table of the Elements; each of X₁ and X₂ represents acarbon atom, a nitrogen atom, or an oxygen atom; L₁, together with X₁and X₂, represents an atom group necessary to form a bidentate ligand;m1 represents an integer of 1 to 3; and m2 represents an integer of 0 to2, provided that a sum of m1 and m2 is 2 or 3.

In Formula (B), substituents represented by R₁, R₂, and R₃ are the sameas those represented by R₁ in the above-described Formula (A). Further,Z, M₁, X₁, X₂, L₁, and the like are also the same as those used inFormula (A), and m1 and m2 are also the same as those used in Formula(A).

A group represented by R₂ of Formula (B) is preferably an aromatichydrocarbocyclic group (an aromatic carbocyclic group), of which asubstituted aryl group is preferred. As the substituted aryl group, agroup represented by Formula (C) below is preferred.

In Formula (C), R₄ represents a substituent having a steric parametervalue (an Es value) of not more than −0.5, R₅ is the same as R₁, and n5represents an integer of 0 to 4. The asterisk “*” in the Formulaindicates a bonding position.

The “Es value” of a substituent denotes a “steric parameter” derivedfrom a chemical reactivity of the substituent. Then, it can be said thatthe smaller the value is, the larger the steric size of the substituentis.

The Es value is explained as follows: It is known that, in general, in ahydrolysis reaction of an ester under an acidic condition, the influencethat a substituent exerts on the progress of the reaction can beconsidered to be only a steric hindrance. Utilizing the abovephenomenon, the steric hindrance of a substituent is numericallyconverted into the Es value.

Es value of substituent X may be obtainable as follows. Reaction rateconstant kX of the following chemical reaction in which α-positionmono-substituted acetate, which is derived from α-positionmono-substituted acetic acid prepared by substituting one hydrogen atomof the methyl group of acetic acid with substituent X, undergoeshydrolysis under acidic conditions, is obtained.X—CH₂COOR_(X)+H₂O→X—CH₂COOH+R_(X)OHReaction rate constant kH of the following reaction (Rx is the same asRy) in which acetate corresponding to the above α-positionmono-substituted acetate undergoes hydrolysis under acetic conditions,is also obtained.CH₃COOR_(Y)+H₂O→CH₃COOH+R_(Y)OH

Subsequently, Es is obtained via the following formula.Es=log(kX/kH)

The reaction rate decreases due to steric hindrance of substituent X. Asa result, since kX<kH is held, Es value commonly becomes negative. Inpractice, when Es value is obtained, two reaction rate constants, namelykX and kH, are determined and it is calculated based on the aboveformula.

Specific examples of Es value are detailed in Unger, S. H., Hansch, C.,Prog. Phys. Org. Chem. 12, 91 (1976). Further, specific numerical valuesare also described in “Yakubutsu no Kozo Kassei Sokan (StructuralActivity Correlation)” (Kagaku no Ryoiki Zokan No. 122, Nanko Do), and“American Chemical Society Professional Reference Book, ‘Exploring QSAR’p. 81, Table 3-3”. Table 1 below shows some of them.

TABLE 1 Es Es Substituent value Substituent value H 0 CH₂OCH₃ −1.43 F−0.46 CH₂NO₂ −2.71 Cl −0.97 CH₂COCH₃ −1.99 Br −1.16 CHF₂ −1.91 I −1.4CHCl₂ −2.78 CH₃ −1.24 CHBr₂ −3.1 C₂H₅ −1.31 CHOHCH₃ −1.15 n-C₃H₇ −1.6CF₃ −2.4 n-C₄H₉ −1.63 CCl₃ −3.3 i-C₄H₉ −2.17 CBr₃ −3.67 s-C₄H₉ −2.37C(C₆H₅)₃ −5.92 t-C₄H₉ −2.78 CHCH₃ −2.84 cyclo-C₄H₇ −1.3 CN −0.51 n-C₅H₁₁−1.64 OH −0.55 i-C₅H₁₁ −1.59 OCH₃ −0.55 CH(C₂H₅) −3.22 SH −1.07cyclo-C₆H₁₁ −2.03 SCH₃ −1.07 CH₂F −1.48 SF₅ −2.91 CH₂Cl −1.48 NH₂ −0.61CH₂Br −1.51 CH₂I −1.61 CH₂OH −1.21

Further, it should be noted that the Es value, which is defined in thepresent invention, is not determined while a methyl group is 0, but isdetermined while a hydrogen atom to be 0, whereby the Es value of thepresent invention is a value which is obtained by subtracting 1.24 fromthe Es value determined while a methyl group is 0.

In the present invention, R₄ is a substituent having an Es value of −0.5or less, preferably it is between −7.0 and −0.6, and it is morepreferably between −7.0 and −1.0.

Further, in the present invention, in the case in which keto-enoltautomers are present in R₄, the Es value of the keto portion isdetermined via conversion as an enol isomer. In cases in which othertautomers are present, Es values are determined based on the sameconversion method.

Examples of phosphorescent compounds of the present inventionrepresented by Formulas (A) or (B) are shown below. However, the presentinvention is not limited by them.

Metal complexes according to an organic EL element material of thisinvention can be synthesized by applying a method described in such asOrganic Letter, vol. 3, No. 16, pp. 2579-2581 (2001), InorganicChemistry vol. 30, No. 8, pp. 1685-1687 (1991), J. Am. Chem. Soc., vol.123, p. 4304 (2001), Inorganic Chemistry vol. 40, No. 7, pp. 1704-1711(2001), Inorganic Chemistry vol. 41, No. 12, pp. 3055-3066 (2002), NewJournal of Chemistry, vol. 26, p. 1171 (2002), European Journal ofOrganic Chemistry Vol. 4, pp. 695-709 (2004), and reference documentsdescribed in these documents.

(Host Compound)

The host compound, employed in the light-emitting layer of the presentinvention, is characterized in that the aforesaid host compoundpreferably has a phosphorescence 0-0 band of a shorter wavelength thanthat of a light-emitting dopant which is employed in combination, andthe phosphorescence 0-0 band thereof is not more than 460 nm. Thephosphorescence 0-0 band of the host compound is preferably not morethan 450 nm, more preferably is not more than 440 nm, and furtherpreferably is not more than 430 nm.

The determination method of the phosphorescence 0-0 band of the presentinvention will be explained. Firstly, a measuring method of aphosphorescence spectrum will be explained.

A host compound to be measured is dissolved in a mixed solvent ofwell-deoxygenated ethanol/methanol (4/1 by volume) and placed in a cellfor phosphorescence measurement, followed by irradiation of excitinglight at a liquid nitrogen temperature of 77 K to measure an emissionspectrum 100 ms after completion of the irradiation of exciting light.It is conceivable that since phosphorescence features a longer emissionlife than fluorescence, most of the light remaining after the 100 mshave elapsed is phosphorescence. Incidentally, a compound exhibiting aphosphorescence life of shorter than 100 ms may be measured byshortening a delay time. However, in cases when shortening the delaytime to the extent that the shortened delay time is not distinguishedfrom the life of fluorescence, a problem occurs in that phosphorescenceand fluorescence each are indistinguishable, and therefore it isnecessary to select an appropriate delay time capable of distinguishingtherebetween.

For a compound insoluble in the solvent system described above, anyappropriate solvent, which can dissolve the compound, may be employed(it is not substantially problematic since a solvent effect on thephosphorescence wavelength in the above measurement method isnegligible.).

Subsequently, a method of determining the 0-0 band is described. In thepresent invention, the 0-0 band is defined as the maximum emissionwavelength appearing in the shortest wavelength portion in thephosphorescence spectrum chart obtained via the above measurementmethod.

Since the intensity of a phosphorescence spectrum is generally weak,when the spectrum is magnified, it becomes difficult, in some cases, todistinguish between a noise band and a signal peak. In such a case, itis possible to determine a targeted signal peak in such a manner that alight emission spectrum generated right after irradiation of excitationlight (for convenience, referred to as “stationary light spectrum”) ismagnified, which is then superimposed on another magnified lightemission spectrum generated at 100 ms after irradiation of excitationlight (for convenience, referred to as “phosphorescence spectrum”), todetect a peak wavelength from the stationary light spectrum originatedin the phosphorescence spectrum. It is also possible to detect a signalpeak wavelength by separation of the noise band and the signal peak viaa smoothing treatment. The smoothing method by Savitzky and Golay may beapplied as the smoothing treatment.

The host compound, employed in the light-emitting layer of the presentinvention, is characterized in that the glass transition point thereofis not less than 60° C. The glass transition point thereof is preferably90° C., more preferably is not more than 130° C., and further preferablyis not more than 160° C.

The glass transition point (Tg) may be determined via a methodconforming to JIS-K-7121 employing the DSC (Differential Scanningcalorimetry).

It is preferable that the above-described host compound, employed in thelight-emitting layer of the present invention, is a compound representedby the above-described Formulae (1) to (7).

(Compounds Represented by Formula (1))

In the above-described Formula (1); R_(1a) represents a hydrogen atom,an aliphatic group, an aromatic group, or a heterocyclic group; each R₁and R₂ independently represents a hydrogen atom or a substituent; andeach n1 and n2 represents an integer of 0 to 4.

Examples of an aliphatic group include: alkyl groups (for example, amethyl group, an ethyl group, a propyl group, an isopropyl group, atert-butyl group, a pentyl group, a hexyl group, an octyl group, adodecyl group, a tridecyl group, a tetradecyl group, and a pentadecylgroup); cycloalkyl groups (for example, a cyclopentyl group, and acyclohexyl group); alkenyl groups (for example, a vinyl group, and anallyl group); and alkynyl groups (for example, an ethynyl group, and apropargyl group).

Examples of an aromatic group include: aromatic hydrocarbocyclic groups(also referred to as an aromatic carbocyclic group or an aryl group,which includes a phenyl group, a p-chlorophenyl group, a mesityl group,a tolyl group, a xylyl group, a naphthyl group, an anthryl group, anazulenyl group, an acenaphthenyl group, a fluorenyl group, a phenanthrylgroup, an indenyl group, a pyrenyl group, and a biphenylyl group);aromatic heterocyclic groups (such as a pyridyl group, a pyrimidinylgroup, a furyl group, a pyrrolyl group, an imidazolyl group, abenzimidazolyl group, a pyrazolyl group, a pyrazinyl group, a triazolylgroup (such as an 1,2,4-triazole-1-yl group, and an 1,2,3-triazole-1-ylgroup), an oxazolyl group, a benzoxazolyl group, a thiazolyl group, anisooxazolyl group, an isothiazolyl group, a furazanyl group, a thienylgroup, a quinolyl group, a benzofuryl group, a dibenzofuryl group, abenzothienyl group, a dibenzothienyl group, an indolyl group, acarbazolyl group, a carbolynyl group, a diazacarbazolyl group (whichindicates a group in which one of carbon atoms constituting a carbolinering of the above-described carbolynyl group is substituted by annitrogen atom), a quinoxalinyl group, a pyridazinyl group, a triazinylgroup, a quinazolinyl group, and a phthalazinyl group.

Examples of a heterocyclic group include a pyrrolidil group, animidazolidyl group, a morpholyl group, and an oxazolidyl group.

The substituent is the same as the substituent represented by R₁ of aphosphorescent compound represented by the above-described Formula (A).

(Compounds Represented by Formula (2))

In the above-described Formula (2); each R₁ and R₂ independentlyrepresents a hydrogen atom, or a substituent; R₃ represents asubstituent; L₁ represents a bivalent linking group; n1 and n2represents an integer of 0 to 4; and m1 represents an integer of 0 to 5.

The substituent represented by R₂ or R₃ is the same as the substituentrepresented by R₁ of a phosphorescent compound represented by theabove-described Formula (A).

The bivalent linking group is formed with an element such as C, N, O, S,Si, or Ge, and is preferably a bivalent aromatic ring, a bivalentaromatic heterocycle, a carbon atom, a nitrogen atom, and a siliconatom.

The bivalent linking group may have the same substituent as thesubstituent explained in the above-described Formula (A). Thesubstituent is preferably an alkyl group, an alkoxyl group, an arylgroup, or a heteroaryl group.

Specific examples of the linking group represented by L₁ are listedbelow, but are not limited to them.

(Compounds Represented by Formula (3))

In the above-described Formula (3); each R₁, R₂ and R₄ independentlyrepresents a hydrogen atom, or a substituent; L₃ represents a bivalentlinking group; Ar₁ represents an aromatic group, or a heterocyclicgroup; n1 to n3 represents an integer of 0 to 4; and m3 represents aninteger of 0 or 1.

The above substituent is the same as the substituent represented by R₁of a phosphorescent compound represented by the above-described Formula(A).

The bivalent linking group is the same as the bivalent linking grouprepresented by L₂ of a compound represented by the above-describedFormula (2).

The aromatic group and the heterocyclic group are the same as thearomatic group and the heterocyclic group represented by R_(1a) of acompound represented by the above-described Formula (1).

(Compounds Represented by Formula (4))

In the above-described Formula (4); R_(1a) represents a hydrogen atom,an aliphatic group, an aromatic group, or a heterocyclic group; each R₁and R₂ represents a substituent; L₃ represents a bivalent linking group;Ar₁ represents an aromatic group, or a heterocyclic group; n1 and n2represents an integer of 0 to 4; and m3 represents an integer of 0 or 1.

The aliphatic group, the aromatic group and the heterocyclic group arethe same as the aliphatic group, the aromatic group and the heterocyclicgroup represented by R_(1a) of a compound represented by theabove-described Formula (1).

The substituent is the same as the substituent represented by R₁ of aphosphorescent compound represented by the above-described Formula (A).

The bivalent linking group is the same as the bivalent linking grouprepresented by L₂ of a compound represented by the above-describedFormula (2).

(Compounds Represented by Formula (5))

In the above-described Formula (5); R_(1a) represents a hydrogen atom,an aliphatic group, an aromatic group, or a heterocyclic group; each R₁and R₂ independently represents a hydrogen atom, or a substituent; L₃represents a bivalent linking group; Ar₁ represents an aromatic group,or a heterocyclic group; n1 represents an integer of 0 to 4; n2represents an integer of 0 to 3; and m3 represents an integer of 0 or 1.

The aliphatic group, the aromatic group and the heterocyclic group arethe same as the aliphatic group, the aromatic group and the heterocyclicgroup represented by R_(1a) of a compound represented by theabove-described Formula (1).

The substituent is the same as the substituent represented by R₁ of aphosphorescent compound represented by the above-described Formula (A).

The bivalent linking group is the same as the bivalent linking grouprepresented by L₂ of a compound represented by the above-describedFormula (2).

(Compounds Represented by Formula (6))

In the above-described Formula (6); R_(1a) represents a hydrogen atom,an aliphatic group, an aromatic group, or a heterocyclic group; each R₁,R₂ and R₅ independently represents a hydrogen atom or a substituent; L₄represents a bivalent linking group; Ar₁ represents an aromatic group ora heterocyclic group; n1 and n4 represents an integer of 0 to 4; n2represents an integer of 0 to 3; and m4 represents an integer of 0 or 1.

The aliphatic group, the aromatic group and the heterocyclic group arethe same as the aliphatic group, the aromatic group and the heterocyclicgroup represented by R_(1a) of a compound represented by theabove-described Formula (1).

The substituent is the same as the substituent represented by R₁ of aphosphorescent compound represented by the above-described Formula (A).

The bivalent linking group is the same as the bivalent linking grouprepresented by L₂ of a compound represented by the above-describedFormula (2).

(Compounds Represented by Formula (7))

In the above-described Formula (7), each R₁, R₂, and Ra independentlyrepresent a hydrogen atom or a substituent, each n1, n2 and narepresents an integer of 0 to 4, and X represents NRb, S, or O,Substituents represented by R₁, R₂ or Ra are the same as thoserepresented by R₁ of the phosphorescent compounds represented by theabove-described Formula (A).

The above-described Rb represents a hydrogen atom, an aliphatic group,an aromatic group, or a heterocyclic group, and is the same as analiphatic group, an aromatic group, or a heterocyclic group representedby R_(1a) in the above-described Formula (1).

Ar₁ in Formulae (3) to (6) is preferably a carbazolyl group.

Specific examples of a host compound represented by Formulae (1) to (6)are listed below, but are not limited to them.

The compounds listed above can be synthesized in accordance withcommonly known methods in this field.

(Light-Emitting Host and Light-Emitting Dopant)

In the organic EL element of the present invention, the light-emittinglayer incorporates a light-emitting host and a light-emitting dopant. Itis preferable that the mixing ratio of the light-emitting dopant to thelight-emitting host which is a main constituent in the light-emittinglayer is controlled in the range of 0.1 to less than 30% by weight.

However, the light-emitting dopant may use a plurality of compounds inmixture, and the compound to be mixed may be other metal complexeshaving a different structure, or a phosphorescent dopant or afluorescent dopant having other structures.

Dopants (such as a phosphorescent dopant or a fluorescent dopant), whichmay be used in combination with a metal complex employed as alight-emitting dopant, will now be explained.

(Light-Emitting Dopant)

The light-emitting dopant is roughly classified into two types: afluorescent dopant which emits fluorescence and a phosphorescent dopantwhich emits phosphorescence.

Representative examples of the former (a fluorescent dopant) include acoumarin dye, a pyran dye, a cyanine dye, a chloconium dye, a squariumdye, an oxobenzanthracene dye, a fluorescein dye, a rhodamine dye, apyrylium dye, a perylene dye, a stilbene dye, a polythiophene dye, and arare earth complex fluorescent material.

Representative examples of the latter (a phosphorescent dopant) arepreferably a complex compound incorporating a metal of Groups 8, 9 and10 of the Periodic Table of the Elements, and more preferably are aniridium, a platinum compound, a ruthenium compound, and a rhodiumcompound, of which an iridium compound, and a platinum compound are morepreferred.

A phosphorescent dopant (also referred to as a phosphorescent compoundor a phosphorescence emission compound) employed in the presentinvention exhibits light emission from an excited triplet. Further, theaforesaid phosphorescent dopant preferably has a phosphorescence quantumyield of not less than 0.001 at 25° C., more preferably of not less than0.01, and particularly preferably of not less than 0.1.

The above-described phosphorescence quantum yield can be determinedaccording to a method described in the fourth edition, Jikken KagakuKoza 7, Bunko II, p. 398 (1992) published by Maruzen. Thephosphorescence quantum yield in a solution can be determined employingvarious kinds of solvents. The aforesaid phosphorescent dopant isacceptable when the above-described phosphorescence quantum yield isachieved in any one or more of the solvents.

A compound represented by Formula (A) of the present invention isemployed as a phosphorescent dopant.

As a phosphorescent dopant other than a compound represented by Formula(A), compounds described in the Patent Documents below are usable.

Such references are as follows: WO 00/70655, JP-A Nos. 2002-280178,2001-181616, 2002-280179, 2001-181617, 2002-280180, 2001-247859,2002-299060, 2001-313178, 2002-302671, 2001-345183 and 2002-324679, WO02/15645, JP-A Nos. 2002-332291, 2002-50484, 2002-332292 and 2002-83684,Japanese Translation of PCT International Application Publication No.2002-540572, JP-A Nos. 2002-117978, 2002-338588, 2002-170684 and2002-352960, WO 01/93642 pamphlet, JP-A Nos. 2002-50483, 2002-100476,2002-173674, 2002-359082, 2002-175884, 2002-363552, 2002-184582 and2003-7469, Japanese Translation of PCT International ApplicationPublication No. 2002-525808, JP-A 2003-7471, Japanese Translation of PCTInternational Application Publication No. 2002-525833, JP-A Nos.2003-31366, 2002-226495, 2002-234894, 2002-235076, 2002-241751,2001-319779, 2001-319780, 2002-62824, 2002-100474, 2002-203679,2002-343572 and 2002-203678.

A part of the specific examples are shown below.

(Light-Emitting Host)

A host compound, employed in the light-emitting layer of the presentinvention, is characterized in that the phosphorescent 0-0 band is notmore than 460 nm as stated before, and the glass transition point is notless than 60° C.

The host compound, employed in the present invention, is a compoundamong those incorporated in a light-emitting layer, which exhibits aphosphorescence quantum yield of phosphorescent emission of less than0.01 at a room temperature (25° C.).

The light-emitting host employed in the present invention is preferablya compound exhibiting a phosphorescence 0-0 band of a wavelength shorterthan that of a light-emitting dopant which is employed in combination.In a case where the light-emitting dopant, incorporating a bluelight-emitting component exhibiting a phosphorescence 0-0 band of notmore than 470 nm, is employed, the light-emitting host preferablyexhibits a phosphorescence 0-0 band of not more than 460 nm.

The above-described host compound, employed in the present invention, ispreferably a compound represented by the above Formulae (1) to (6).

Further, the light-emitting host, employed in the present invention, isnot particularly limited by its chemical structure as long as thephosphorescent 0-0 band is not more than 460 nm as stated before, andthe glass transition point is not less than 60° C., and may be a lowmolecular weight compound or a high molecular weight compound having arepeating unit, and may further be a low molecular weight compoundhaving a polymerizable group such as a vinyl group and an epoxy group(an vapor-deposition polymerizable light-emitting host). Among thosehosts, preferable are compounds having hole transporting capability andelectron transporting capability, while preventing elongation of theemission wavelength, and further having a higher Tg (a glass transitiontemperature).

Representative light-emitting hosts of the present invention include;compounds having the basic skeletons such as a carbazole derivative, atriarylamine derivative, an aromatic borane derivative, anitrogen-containing heterocyclic compound, a thiophene derivative, afuran derivative, and an oligoarylene compound; or derivatives having aring structure in which at least one of carbon atoms of a hydrocarbonring, which constitutes a carboline derivative or a carboline ring ofthe aforesaid carboline derivative, is substituted with a nitrogen atom.

Specific examples of the light-emitting host include, but are notlimited to, compounds described in the following Patent Documents; JP-ANos. 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357977,2002-334786, 2002-8860, 2002-334787, 2002-15871, 2002-334788,2002-43056, 2002-334789, 2002-75645, 2002-338579, 2002-105445,2002-343568, 2002-141173, 2002-352957, 2002-203683, 2002-363227,2002-231453, 2003-3165, 2002-234888, 2003-27048, 2002-255934,2002-260861, 2002-280183, 2002-299060, 2002-302516, 2002-305083,2002-305084, and 2002-308837.

Next, representative structures of organic EL elements will bedescribed.

<Constituent Layers of Organic EL Element>

Typical constitutions of an organic EL element of the present inventionwill be described. Specific examples of a preferable layer constitutionof an organic EL element of this invention are shown below; however, thepresent invention is not limited thereto.

(i) anode/positive hole transport layer/emission layer/positive holeinhibition layer/electron transport layer/cathode,

(ii) anode/positive hole transport layer/electron inhibitionlayer/emission layer/positive hole inhibition layer/electron transportlayer/cathode,

(iii) anode/positive hole transport layer/electron inhibitionlayer/emission layer/positive hole inhibition layer/electron transportlayer/cathode,

(iv) anode/anode buffer layer/positive hole transport layer/electroninhibition layer/interlayer/emission layer/positive hole inhibitionlayer/electron transport layer/cathode,

(v) anode/positive hole transport layer/electron inhibitionlayer/emission layer/positive hole inhibition layer/electron transportlayer/cathode buffer layer/cathode,

<Inhibition Layer (Electron Inhibition Layer, Positive Hole InhibitionLayer)>

An inhibition layer (such as an electron inhibition layer, a positivehole inhibition layer) according to this invention will now beexplained.

The layer thickness of an inhibition layer according to this inventionis preferably 3-100 nm and more preferably 5-30 nm.

<Positive Hole Inhibition Layer>

A positive hole inhibition layer, in a broad meaning, is provided with afunction of electron transport layer, being comprised of a materialhaving a function of transporting an electron but a very small abilityof transporting a positive hole, and can improve the recombinationprobability of an electron and a positive hole by inhibiting a positivehole while transporting an electron.

As a positive hole inhibition layer, for example, a positive inhibitionlayer described in such as JP-A Nos. 11-204258 and 11-204359 and p. 237of “Organic EL Elements and Idustrialization Front Thereof (Nov. 30(1998), published by N. T. S Corp.)” is applicable to a positive holeinhibition (hole block) layer according to this invention. Further, aconstitution of an electron transport layer described later can beappropriately utilized as a positive hole inhibition layer according tothis invention.

Specific examples are cited below, but the present invention is notlimited to them.

<Electron Inhibition Layer>

On the other hand, an electron inhibition layer is, in a broad meaning,provided with a function of a positive hole transport layer, beingcomprised of a material having a function of transporting a positivehole but a very small ability of transporting an electron, and canimprove the recombination probability of an electron and a positive holeby inhibiting an electron while transporting a positive hole. Further, aconstitution of a positive hole transport layer described later can beappropriately utilized as an electron inhibition layer.

<Positive Hole Transport Layer>

A positive hole transport layer contains a material having a function oftransporting a positive hole, and in a broad meaning, a positive holeinjection layer and an electron inhibition layer are also included in apositive hole transport layer. A single layer of or plural layers of apositive hole transport layer may be provided.

A positive hole transport material is not specifically limited and canbe arbitrary selected from those such as generally utilized as a chargeinjection transporting material of a positive hole in a conventionalphotoconductive material and those which are well known in the art andutilized in a positive hole injection layer and a positive holetransport layer of an EL element.

A positive hole transport material is those having any one of a propertyto inject or transport a positive hole or a barrier property to anelectron, and may be either an organic substance or an inorganicsubstance. For example, listed are a triazole derivative, an oxadiazolederivative, an imidazole derivative, a polyallylalkane derivative, apyrazolone derivative, a phenylenediamine derivative, a allylaminederivative, an amino substituted chalcone derivative, an oxazolederivatives, a styrylanthracene derivative, a fluorenone derivative, ahydrazone derivative, a stilbene derivative, a silazane derivative, ananiline type copolymer, or conductive polymer oligomer and specificallypreferably such as thiophene oligomer.

As a positive hole transport material, those described above can beutilized, however, it is preferable to utilized a porphyrin compound, anaromatic tertiary amine compound and a styrylamine compound, andspecifically preferably an aromatic tertiary amine compound.

Typical examples of an aromatic tertiary amine compound and astyrylamine compound include N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl;N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(TDP); 2,2-bis(4-di-p-tolylaminophenyl)propane;1,1-bis(4-di-p-tolylaminophenyl)cyclohexane; N,N,N′,N′-tetra-p-tolyl 4,4′-diaminobiphenyl;1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;bis(4-dimethylamino-2-methyl)phenylmethane;bis(4-di-p-tolylaminophenyl)phenylmethane;N,N′-diphenyl-N,N′-di(4-methoxyphenyl)-4,4′-diaminobiphenyl;N,N,N′,N′-tetraphenyl-4,4′-diaminophenylether;4,4′-bis(diphenylamino)guarterphenyl; N,N,N-tri(p-tolyl)amine;4-(di-p-tolylamino)-4′-[4-(di-p-triamino)styryl]stilbene;4-N,N-diphenylamino-(2-diphenylvinyl)benzene;3-methoxy-4′-N,N-diphenylaminostilbene; and N-phenylcarbazole, inaddition to those having two condensed aromatic rings in a moleculedescribed in U.S. Pat. No. 5,061,569, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NDP), and4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MDTDATA),in which three of triphenylamine units are bonded in a star burst form,described in JP-A 4-308688.

Polymer materials, in which these materials are introduced in a polymerchain or constitute the main chain of polymer, can be also utilized.

Further, an inorganic compound such as a p type-Si and a p type-SiC canbe utilized as a positive hole injection material and a positive holetransport material

This positive hole transport layer can be prepared by forming a thinlayer made of the above-described positive hole transport materialaccording to a method well known in the art such as a vacuum evaporationmethod, a spin coating method, a cast method, an inkjet method and a LBmethod. The layer thickness of a positive hole transport layer is notspecifically limited, however, is generally 5-5,000 nm. This positivetransport layer may have a single layer structure comprised of one ornot less than two types of the above described materials.

<Electron Transport Layer>

An electron transfer layer is composed of a material having a functionto transfer an electron, and an electron injection layer and a positivehole inhibition layer are included in an electron transfer layer in abroad meaning. A single layer or plural layers of an electron transferlayer may be provided.

Further, an electron transfer layer is provided with a function totransmit an electron injected from a cathode to an emission layer, andcompounds conventionally well known in the art can be utilized byarbitrarily selection as a material thereof.

Examples of a material utilized in this electron transfer layer(hereinafter, referred to as an electron transfer material) include suchas a nitro-substituted fluorene derivative, a diphenylquinonederivative, a thiopyradineoxide derivative, a heterocyclic tetracarbonicacid anhydride such as naphthaleneperylene, carbodiimide, afluorenylidenemethane derivative, anthraquinonedimethane and anthronederivatives, and an oxadiazole derivative. Further, a thiazolederivative in which an oxygen atom in the oxadiazole ring of theabove-described oxadiazole derivative is substituted by a sulfur atom,and a quinoxaline derivative having a quinoxaline ring which is known asan electron attracting group can be utilized as an electron transfermaterial.

Polymer materials, in which these materials are introduced in a polymerchain or these materials form the main chain of polymer, can be alsoutilized.

Further, a metal complex of a 8-quinolinol derivative such astris(8-quinolinol)aluminum (Alq),tris(5,7-dichloro-8-quinolinol)aluminum,tris(5,7-dibromo-8-quinolinol)aluminum,tris(2-methyl-8-quinolinol)aluminum, tris(5-methyl-8-quinolinol)aluminumand bis(8-quinolinol)zinc (Znq); and metal complexes in which a centralmetal of the aforesaid metal complexes is substituted by In, Mg, Cu, Ca,Sn, Ga or Pb, can be also utilized as an electron transfer material.

Further, metal-free or metal phthalocyanine, or those the terminal ofwhich is substituted by an alkyl group and a sulfonic acid group, can bepreferably utilized as an electron transfer material. Further,distyrylpyrazine derivative, which has been exemplified as a material ofan emission layer, can be also utilized as an electron transfermaterial, and, similarly to the case of a positive hole injection layerand a positive hole transfer layer, an inorganic semiconductor such asan n-type-Si and an n-type-SiC can be also utilized as an electrontransfer material.

This electron transport layer can be prepared by forming a thin layermade of the above-described electron transport material according to amethod well known in the art such as a vacuum evaporation method, a spincoating method, a cast method, an inkjet method and a LB method. Thelayer thickness of an electron transport layer is not specificallylimited; however, is generally 5-5,000 nm. This electron transport layermay have a single layer structure comprised of one or not less than twotypes of the above described materials.

In the following, injection layer of a display device provided with anorganic EL element of this invention will be explained.

<Injection Layer>: Electron Injection Layer, Positive Hole InjectionLayer

An injection layer is appropriately provided and includes an electroninjection layer and a positive hole injection layer, which may bearranged between an anode and an emission layer or a positive transferlayer, and between a cathode and an emission layer or an electrontransfer layer, as described above.

An injection layer is a layer which is arranged between an electrode andan organic layer to decrease an operating voltage and to improve anemission luminance, which is detailed in volume 2, chapter 2 (pp.123-166) of “Organic EL Elements and Industrialization Front thereof(Nov. 30th 1998, published by N. T. S Corp.)”, and includes a positivehole injection layer (an anode buffer layer) and an electron injectionlayer (a cathode buffer layer).

An anode buffer layer (a positive hole injection layer) is also detailedin such as JP-A 9-45479, 9-260062 and 8-288069, and specific examplesinclude such as a phthalocyanine buffer layer comprising such as copperphthalocyanine, an oxide buffer layer comprising such as vanadium oxide,an amorphous carbon buffer layer, and a polymer buffer layer employingconductive polymer such as polythiophene.

A cathode buffer layer (an electron injection layer) is also detailed insuch as JP-A 6-325871, 9-17574 and 10-74586, and specific examplesinclude a metal buffer layer comprising such as strontium and aluminum,an alkali metal compound buffer layer comprising such as lithiumfluoride, an alkali earth metal compound buffer layer comprising such asmagnesium fluoride, and an oxide buffer layer comprising such asaluminum oxide.

The above-described buffer layer (injection layer) is preferably a verythin layer, and the layer thickness is preferably in a range of 0.1-100nm although it depends on a raw material.

This injection layer can be prepared by forming a thin layer made of theabove-described material according to a method well known in the artsuch as a vacuum evaporation method, a spin coating method, a castmethod, an inkjet method and a LB method. The layer thickness of aninjection layer is not specifically limited; however, is generally5-5,000 nm. This injection layer may have a single layer structurecomprised of one or not less than two types of the above describedmaterials.

<Anode>

As an anode according to an organic EL element of this invention, thosecomprising metal, alloy, a conductive compound, which is provided with alarge work function (not less than 4 eV), and a mixture thereof as anelectrode substance are preferably utilized. Specific examples of suchan electrode substance include a conductive transparent material such asmetal like Au, CuI, indium tin oxide (ITO), SnO₂ and ZnO. Further, amaterial such as IDIXO (In₂O₃—ZnO), which can prepare an amorphous andtransparent electrode, may be also utilized. As for an anode, theseelectrode substances may be made into a thin layer by a method such asevaporation or spattering and a pattern of a desired form may be formedby means of photolithography, or in the case of requirement of patternprecision is not so severe (not less than 100 μm), a pattern may beformed through a mask of a desired form at the time of evaporation orspattering of the above-described substance. When emission is taken outof this anode, the transmittance is preferably set to not less than 10%and the sheet resistance as an anode is preferably not more than a fewhundreds Ω/□. Further, although the layer thickness depends on amaterial, it is generally selected in a range of 10-1,000 nm andpreferably of 10-200 nm.

<Cathode>

On the other hand, as a cathode according to this invention, metal,alloy, a conductive compound and a mixture thereof, which have a smallwork function (not more than 4 eV), are utilized as an electrodesubstance. Specific examples of such an electrode substance includessuch as sodium, sodium-potassium alloy, magnesium, lithium, amagnesium/copper mixture, a magnesium/silver mixture, amagnesium/aluminum mixture, a magnesium/indium mixture, analuminum/aluminum oxide (Al₂O₃) mixture, indium, a lithium/aluminummixture and rare earth metal. Among them, with respect to an electroninjection property and durability against such as oxidation, preferableare a mixture of electron injecting metal with the second metal which isstable metal having a work function larger than electron injectingmetal, such as a magnesium/silver mixture, a magnesium/aluminum mixture,a magnesium/indium mixture, an aluminum/aluminum oxide (Al₂O₃) mixtureand a lithium/aluminum mixture, and aluminum.

As for a cathode, these electrode substances may be made into a thinlayer by a method such as evaporation or spattering. Further, the sheetresistance as a cathode is preferably not more than a few hundreds Ω/□and the layer thickness is generally selected in a range of 10-1,000 nmand preferably of 50-200 nm. Herein, to transmit emission, either one ofan anode or a cathode of an organic EL element is preferably transparentor translucent to improve the mission luminance.

<Substrate (Also Referred to as Base Plate, Base Material or Support)>

A substrate according to an organic EL element of this invention is notspecifically limited with respect to types of such as glass and plasticsprovided being transparent, however, a substrate preferably utilizedincludes such as glass, quartz and transparent resin film. Aspecifically preferable substrate is resin film capable of providing anorganic EL element with a flexible property.

Resin film includes such as film comprised of polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyether sulphone (PES),polyether imide, polyether etherketone, polyphenylene sulfide,polyallylate, polyimide, polycarbonate (PC) and cellulose acetatepropionate (CAP).

On the surface of resin film, an inorganic or organic cover layer or ahybrid cover layer comprising the both may be formed, and the film ispreferably provided with a high barrier ability having a vaportransmittance of not more than 0.01 g/m²·day·at atm.

The taking out efficiency of emission of an organic EL element of thisinvention at room temperature is preferably not less than 1% and morepreferably not less than 2%. Herein, taking out quantum efficiency(%)=photon number emitted out of organic EL element/electron numberflown into organic EL element×100.

Further, a hue improving filter such as a color filter may be utilizedin combination. In the case of an illumination application, rougheningprocessed film (such as anti-glare film) can be also utilized incombination to decrease emission unevenness.

In the case of an application as a multi-color display device, thedisplay is comprised of at least two types of organic EL elements havingdifferent emission maximum wavelengths, and a preferable example toprepare an organic EL element will now be explained.

<Preparation Method of Organic EL Element>

As an example of claimed invention, a preparation method of an organicEL element, comprising anode/positive hole injection layer/positive holetransport layer/emission layer/positive hole inhibition layer/electrontransport layer/cathode buffer layer/cathode, will be explained.

First, on an appropriate substrate, a thin layer comprising a desiredelectrode substance such as an anode electrode substance is formed bymeans of evaporation or spattering so as to make a layer thickness ofnot more than 1 μm and preferably of 10-200 nm, whereby an anode isprepared. Next, on this layer, thin layers containing organic substancesof such as a positive hole injection layer, a positive hole transportlayer, an emission layer, a positive hole inhibition layer and anelectron transport layer are formed.

A thin layer forming method of these layers containing the organicsubstances includes such as a spin coat method, a cast method, an inkjetmethod, an evaporation method and a printing method as described before,however, a vacuum evaporation method or a spin coat method isspecifically preferable with respect to easy preparation of ahomogeneous layer and bare generation of pinholes. Further, a differentlayer forming method depending on each layer may be applied. In the caseof employing an evaporation method in layer formation, the evaporationcondition depends on such as the type of a utilized compound, however,is generally appropriately selected in a range of 50-450° C. as a boatheating temperature, 10⁻⁶-10⁻² Pa as a vacuum degree, 0.01-50 nm/sec asa deposition rate, −50-300° C. as a substrate temperature and 0.1-5 μmas a layer thickness.

After formation of these layers, a thin layer comprising a cathodeelectrode substance is formed thereon by means of such as evaporation orspattering so as to make a layer thickness of less than 1 μm orpreferably in a range of 50-200 nm to provide a cathode, whereby adesired organic EL element can be prepared. This preparation of anorganic EL element is preferably carried out with one time evacuation toprepare all through from a positive hole injection layer to a cathode,however, different layer forming method may be also applied by takingout the element on the way. At that time, it is preferable to takeconsideration such as to perform the operation under a dry inert gasenvironment.

<Display Device>

A display device of this invention will now be explained. The displaydevice of this invention includes the above-described organic ELelement.

A display device of this invention may be either monochromatic ormulti-colored. Here explained will be a multicolor display device. Inthe case of a multicolor display device, a shadow mask is provided onlyat the time of emission layer formation, and layers can be formed allover the surface by such as an evaporation method, a cast method, a spincoat method, an inkjet method and a printing method.

When patterning is performed only with an emission layer, the method isnot specifically limited; however, preferable are an evaporation method,an inkjet method and a printing method. And patterning employing ashadow mask is preferred in the case of an evaporation method. Further,reversing the preparation order, it is also possible to prepare layersin the order of a cathode, an electron transport layer, a positive holeinhibition layer, an emission layer, a positive hole transport layer andan anode.

When a direct current voltage is applied on the multicolor displaydevice thus prepared, emission can be observed by application of avoltage of approximately 2-40 V setting an anode to + polarity and acathode to − polarity. Further, no current flows and no emissiongenerate at all even when a voltage is applied with a reversed polarity.Further, in the case of alternate current voltage being applied,emission generates only in a state of an anode being + and a cathodebeing −. Herein, the wave shape of alternate current may be arbitrary.

A multicolor display device can be utilized as a display device, adisplay and various types of emission light sources. In a display deviceand a display, full-colored display is possible by employing three typesof organic EL elements providing blue, red and green emissions. Adisplay device and a display include a TV, a personal computer, a mobileinstrument, an AV instrument, a character broadcast display and aninformation display in a car. Particularly, the display device and thedisplay may be also utilized as a display to playback still images andmoving images, and may adopt either a simple matrix (a passive matrix)mode or an active matrix mode when being utilized as a display devicefor moving image playback.

An illumination light source includes a home use illumination, a carroom illumination, a backlight of a watch or a liquid crystal, a paneladvertisement, a signal, a light source of an optical memory medium, alight source for an electrophotographic copier, a light source for anoptical telecommunication processor and a light source for aphoto-sensor, however, is not limited thereto.

<Illumination Device>

An illumination device of this invention will now be explained. Theillumination device of this invention includes the above-describedorganic EL element.

An organic EL element of this invention can be utilized as an organic ELelement provided with a resonator structure, and a utilization purposeof such an organic EL element provided with a resonator structureincludes such as a light source for an optical memory medium, a lightsource for an electrophotographic copier, a light source for a opticaltelecommunication processor and a light source for a photo-sensor,however, is not limited thereto. Further, the organic EL element may beutilized for the above-described applications by being made to performlaser emission.

Further, an organic EL element of this invention may be utilized as onetype of a lamp like an illumination and an exposure light, and may bealso utilized as a display device of a projector of an image projectingtype and a display device (a display) of a type to directly view stillimages and moving images. An operating mode in the case of beingutilized as a display device for playback of moving images may be eithera simple matrix (a passive matrix) mode or an active matrix mode. Inaddition, a full-color display device can be prepared by utilizing atleast two types of organic EL elements of this invention which emitdifferent emitting colors.

In the following, one example of a display device provided with anorganic EL element of this invention will be explained.

FIG. 1 is a schematic drawing to show an example of a display deviceconstituted of an organic EL element. It is a schematic drawing of adisplay, which displays image information by emission of an organic ELelement, such as a mobile phone. Display 1 is constituted of such asdisplay section A having plural number of pixels and control section Bwhich performs image scanning of display section A based on imageinformation.

Control section B, which is electrically connected to display section A,sends a scanning signal and an image data signal to plural number ofpixels based on image information from the outside and pixels of eachscanning line successively emit depending on the image data signal by ascanning signal to perform image scanning, whereby image information isdisplayed on display section A.

FIG. 2 is a schematic drawing of display section A.

Display section A is provided with such as a wiring part, which containsplural scanning lines 5 and data lines 6, and plural pixels 3 on asubstrate. Primary part materials of display section A will be explainedin the following.

In the drawing, shown is the case that light emitted by pixel 3 is takenout along the white allow (downward).

Scanning lines 5 and plural data lines 6 in a wiring part each arecomprised of a conductive material, and scanning lines 5 and data lines6 are perpendicular in a grid form and are connected to pixels 3 at theright-angled crossing points (details are not shown in the drawing).

Pixel 3 receives an image data from data line 6 when a scanning signalis applied from scanning line 5 and emits according to the receivedimage data. Full-color display device is possible by appropriatelyarranging pixels having an emission color in a red region, pixels in agreen region and pixels in a blue region, side by side on the samesubstrate.

Next, an emission process of a pixel will be explained.

FIG. 3 is a schematic drawing of a pixel.

A pixel is equipped with such as organic EL element 10, switchingtransistor 11, operating transistor 12 and capacitor 13. Red, green andblue emitting organic EL elements are utilized as organic EL element 10for plural pixels, and full-color display device is possible byarranging these side by side on the same substrate.

In FIG. 3, an image data signal is applied on the drain of switchingtransistor 11 via data line 6 from control section B. Then, when ascanning signal is applied on the gate of switching transistor 11 viascanning line 5 from control section B, operation of switchingtransistor is on to transmit the image data signal applied on the drainto the gates of capacitor 13 and operating transistor 12.

Operating transistor 12 is on, simultaneously with capacitor 13 beingcharged depending on the potential of an image data signal, bytransmission of an image data signal.

In operating transistor 12, the drain is connected to electric sourceline 7 and the source is connected to the electrode of organic ELelement 10, and an electric current is supplied from electric sourceline 7 to organic EL element 10 depending on the potential of an imagedata applied on the gate.

When a scanning signal is transferred to next scanning line 5 bysuccessive scanning of control section B, operation of switchingtransistor 11 is off. However, since capacitor 13 keeps the chargedpotential of an image data signal even when operation of switchingtransistor 11 is off, operation of operating transistor 12 is kept on tocontinue emission of organic EL element 10 until the next scanningsignal is applied. When the next scanning signal is applied bysuccessive scanning, operating transistor 12 operates depending on thepotential of an image data signal synchronized to the scanning signaland organic EL element 10 emits.

That is, emission of each organic EL element 10 of plural pixels 3 isperformed by providing switching transistor 11 and operating transistor12 against each organic EL element 10 of plural pixels 3. Such anemission method is called as an active matrix mode.

Herein, emission of organic EL element 10 may be either emission ofplural gradations based on a multiple-valued image data signal havingplural number of gradation potentials or on and off of a predeterminedemission quantity based on a binary image data signal. Further,potential hold of capacitor 13 may be either continuously maintaineduntil the next scanning signal application or discharged immediatelybefore the next scanning signal application.

In this invention, emission operation is not necessarily limited to theabove-described active matrix mode but may be a passive matrix mode inwhich organic EL element is emitted based on a data signal only when ascanning signal is scanned.

FIG. 4 is a schematic drawing of a display device based on a passivematrix mode. In FIG. 4, plural number of scanning lines 5 and pluralnumber of image data lines 6 are arranged grid-wise, opposing to eachother and sandwiching pixels 3.

When a scanning signal of scanning line 5 is applied by successivescanning, pixel 3 connected to scanning line 5 applied with said signalemits depending on an image data signal.

Since pixel 3 is provided with no active element in a passive matrixmode, decrease of manufacturing cost is possible.

An organic EL element material described in the claimed this inventioncan be also applied to an organic EL element to generate emission ofpractically white color as an illumination device. Plural emissioncolors are simultaneously emitted by plural number of emission materialsto obtain white light by mixing colors. A combination of plural emissioncolors may be either the one, in which three emission maximumwavelengths of three primary colors of blue, green and red arecontained, or the other, in which two emission maximum wavelengths,utilizing a relationship of complimentary colors such as blue andyellow, or blue and orange, are contained.

Further, a combination of emission materials to obtain plural number ofemission colors may be either a combination comprising plural number ofmaterials which emit phosphoresce or fluorescence, or a combination of amaterial which emits phosphoresce or fluorescence and a dye materialwhich emits by light from an emission material as exiting light,however, in a white organic electroluminescent element according to thisinvention, it is enough only to mix plural emission dopants incombination. A mask is provided only at the time of forming such as anemission layer, a positive hole transport layer or an electron transportlayer, to only simply arrange the plural emission dopants such as byseparately painting through the mask, while other layers are commonlyutilized to require no patterning such as a mask. Therefore, such as anelectrode can be formed all over the plane by such as an evaporationmethod, a cast method, a spin coat method, an inkjet method and aprinting method, resulting in improvement of productivity. According tothis method, different from a white organic EL device in which pluralcolors of emission elements are arranged parallel in an alley form, anelement itself is white emitting.

An emission material utilized in an emission layer is not specificallylimited, and in the case of a backlight of a liquid crystal displayelement, any combination by arbitrary selection among platinum complexesaccording to this invention or emission materials well known in the artcan be utilized so as to be fitted to the wavelength range correspondingto CF (color filter) characteristics, whereby white emission can beobtained.

In this manner, a white emitting organic EL element having a structureof claims 1-4 and 13-18 of this invention is usefully utilized as onetype of a lamp such as a home use illumination, a car room illuminationor an exposure light source as various emission light sources orillumination devices, in addition to the aforesaid display device and adisplay, and is further usefully applied for a display as such as abacklight of a liquid crystal display.

In addition to these, listed is a wide range of applications such as abacklight of a watch, an advertising board, a signal, a light source ofan optical memory medium, a light source of an electrophotographiccopier, a light source of an optical telecommunication processor and alight source of an optical sensor, and further general home use electricinstruments which require a display device.

EXAMPLES

The present invention is described below with reference to examples, butthe embodiment of the invention is not limited to them.

Example 1 Preparation of Organic EL Elements 1-1 to 1-41

A pattern was formed on a substrate composed of a glass plate of 100mm×100 mm×1.1 mm and a 100 nm ITO (indium tin oxide) layer (NA45:manufactured by NH Technoglass Co., Ltd.) as an anode. Then theresulting transparent substrate, having the above ITO transparentelectrode, was subjected to ultrasonic cleaning in iso-propylalcohol,dried with a dry nitrogen gas, and then subjected to UV-ozone cleaningfor 5 minutes. Thus obtained transparent substrate was fixed to asubstrate holder of a commercially available vacuum depositionapparatus. Further, 200 mg of α-NPD was placed in a first resistiveheating molybdenum boat, 200 mg of CBP, as a host compound, was placedin a second resistive heating molybdenum boat, 200 mg of BCP was placedin a third resistive heating molybdenum boat, 100 mg of illustratedcompound 1-1 was placed in a fourth resistive heating molybdenum boat,and 200 mg of Alq₃ was placed in a fifth resistive heating molybdenumboat, and the resulting boats were fixed in the vacuum depositionapparatus.

After the pressure in the vacuum tank was reduced to 4×10⁻⁴ Pa, theabove heating boat carrying α-NPD was heated by applying an electriccurrent to evaporate α-NPD onto the transparent substrate at adeposition rate of 0.1 nm/sec to form a positive hole transport layer of40 nm in thickness. Further, the above heating boats, each carrying CBPand illustrated compound 1-1, were heated by applying an electriccurrent to co-evaporate CBP and illustrated compound 1-1 onto theabove-described positive hole transport layer at a deposition rate of0.2 nm/sec and 0.012 nm/sec respectively to form a light-emitting layerof 40 nm in thickness. The temperature of the substrate duringdeposition was room temperature. Further, the above heating boatcarrying BCP was heated by applying an electric current to evaporate BCPonto the above-described light-emitting layer at a deposition rate of0.1 nm/sec to form an electron transport layer of 10 nm in thickness.The resulting electron transport layer also functioned as a holeblocking layer. Furthermore, the above heating boat carrying Alq₃ washeated by applying an electric current to evaporate Alq₃ onto theabove-described electron transport layer at a deposition rate of 0.1nm/sec to form an electron injection layer of 40 nm in thickness.Temperature of the substrate during deposition was room temperature.

Subsequently, a cathode was prepared by evaporating lithium fluoride andaluminum onto the above sample with 0.5 nm and 110 nm in thicknessrespectively, to prepare organic EL element 1-1.

Organic EL elements 1-2 to 1-41 were prepared in the same manner as inpreparation of organic EL element 1-1 except that CBP, which wasemployed as a host compound in a light-emitting layer, was changed tothose compounds given in Tables 2 and 3, and illustrated compound 1-1,which was employed as a dopant compound in a light-emitting layer, waschanged to those compounds given in Tables 2 and 3. The structures ofcompounds employed in the foregoing description are shown below.

Evaluations of Organic EL Elements 1-1 to 1-41

The prepared organic EL elements 1-1 to 1-41 were evaluated in thefollowing way, with the results shown in Tables 2 and 3.

(External Quantum Efficiency)

External quantum efficiency (%) of each of the prepared organic ELelements was determined with a constant current of 2.5 mA/cm² beingsupplied to each of the samples at 23° C. in a dry nitrogen gasatmosphere. A spectroradiometer CS-1000 (manufactured by Konica Minolta)was used for the measurement.

External quantum efficiency given in Tables 2 and 3 was expressed by arelative value based on the external quantum efficiency of organic ELelement 1-1 being 100.

(Emission Life)

A period in which brightness of an organic EL element, when driven atconstant current of 2.5 mA/cm², decreased to half of the brightnessimmediately after the initiation of emission (initial brightness) wasdetermined, and the period was defined as the half-life period (T 0.5)and used as an index of the life of an organic EL element. Aspectroradiometer CS-1000 (manufactured by Konica Minolta) was used forthe measurement.

In Tables 2 and 3, emission life was expressed by a relative value basedon the emission life of organic EL element 1-1 being 100.

TABLE 2 Organic EL Dopant Compound Host Compound External Element Com-HOMO LUMO Com- T1 Tg Quantum No. pound (eV) (eV) pound (nm) (° C.)Efficiency Life Note 1-1 1-1 −4.37 −0.57 CBP 465 109 100 100 Comp. 1-21-2 −4.53 −0.76 CBP 465 109 98 115 Comp. 1-3 1-5 −4.18 −0.42 CBP 465 109105 90 Comp. 1-4 1-1 −4.37 −0.57 H-1 411 64 163 120 Inv. 1-5 1-2 −4.53−0.76 H-1 411 64 155 131 Inv. 1-6 1-5 −4.18 −0.42 H-1 411 64 164 115Inv. 1-7 1-1 −4.37 −0.57 H-20 437 92 144 150 Inv. 1-8 1-2 −4.53 −0.76H-20 437 92 150 155 Inv. 1-9 1-1 −4.37 −0.57 H-19 445 130 148 173 Inv.1-10 1-2 −4.53 −0.76 H-19 445 130 155 180 Inv. 1-11 1-1 −4.37 −0.57 H-18446 180 156 177 Inv. 1-12 1-2 −4.53 −0.76 H-18 446 180 171 179 Inv. 1-131-1 −4.37 −0.57 H-21 449 80 159 130 Inv. 1-14 1-2 −4.53 −0.76 H-21 44980 155 132 Inv. 1-15 1-1 −4.37 −0.57 H-29 449 142 160 155 Inv. 1-16 1-2−4.53 −0.76 H-29 449 142 149 163 Inv. 1-17 FIrpic −5.99 −2.36 H-1 411 64153 50 Comp. 1-18 FIrpic −5.99 −2.36 CBP 465 109 96 70 Comp. 1-19 1-20−5.02 −1.2 CBP 465 109 93 90 Comp. 1-20 1-20 −5.02 −1.2 H-1 411 64 141120 Inv. 1-21 1-20 −5.02 −1.2 H-20 437 92 139 139 Inv. 1-22 1-20 −5.02−1.2 H-19 445 130 137 145 Inv. 1-23 1-20 −5.02 −1.2 H-18 446 180 135 150Inv. 1-24 1-20 −5.02 −1.2 H-21 449 80 145 127 Inv. 1-25 1-20 −5.02 −1.2H-29 449 142 141 136 Inv. 1-26 1-31 −4.7 −0.67 CBP 465 109 89 101 Comp.1-27 1-31 −4.7 −0.67 H-1 411 64 130 129 Inv. 1-28 1-31 −4.7 −0.67 H-20437 92 125 134 Inv. 1-29 1-31 −4.7 −0.67 H-19 445 130 123 152 Inv. 1-301-31 −4.7 −0.67 H-18 446 180 120 155 Inv. 1-31 1-31 −4.7 −0.67 H-21 44980 139 130 Inv. 1-32 1-31 −4.7 −0.67 H-29 449 142 135 132 Inv. T1:Phosphorescent 0-0 Band Comp.: Comparative Example, Inv.: PresentInvention

TABLE 3 Organic EL Dopant Compound Host Compound External Element Com-HOMO LUMO Com- T1 Tg Quantum No. pound (eV) (eV) pound (nm) (° C.)Efficiency Life Note 1-33 1-75 −4.34 −0.55 H-32 437 166 158 190 Inv.1-34 1-77 −4.36 −0.66 H-32 437 166 155 185 Inv. 1-35 1-79 −4.26 −0.47H-32 437 166 148 169 Inv. 1-36 1-75 −4.34 −0.55 H-36 416 169 166 195Inv. 1-37 1-75 −4.34 −0.55 H-37 443 143 160 188 Inv. 1-38 1-77 −4.36−0.66 H-36 416 169 157 191 Inv. 1-39 1-77 −4.36 −0.66 H-37 443 143 152182 Inv. 1-40 1-79 −4.26 −0.47 H-36 416 169 147 172 Inv. 1-41 1-79 −4.26−0.47 H-37 443 143 144 166 Inv. T1: Phosphorescent 0-0 Band Inv.:Present Invention

Tables 2 and 3 show that the organic EL elements of the presentinvention achieved high external quantum efficiency and long life.

Example 2 Preparation of Organic EL Elements 2-1 to 2-45

A pattern was formed on a substrate composed of a glass plate of 100mm×100 mm×1.1 mm and a 100 nm ITO (indium tin oxide) layer (NA45:manufactured by NH Technoglass Co., Ltd.) as an anode. Then theresulting transparent substrate, having the above ITO transparentelectrode, was subjected to ultrasonic cleaning in iso-propylalcohol,dried with a dry nitrogen gas, and then subjected to UV-ozone cleaningfor 5 minutes. Thus obtained transparent substrate was fixed to asubstrate holder of a commercially available vacuum depositionapparatus. Further, 200 mg of α-NPD was placed in a first resistiveheating molybdenum boat, 100 mg of illustrated compound H-21, as anelectron blocking compound, was placed in a second resistive heatingmolybdenum boat, 200 mg of CBP, as a host compound was placed in a thirdresistive heating molybdenum boat, 200 mg of BCP was placed in a fourthresistive heating molybdenum boat, 100 mg of illustrated compound 1-1was placed in a fifth resistive heating molybdenum boat, and 200 mg ofAlq₃ was placed in a sixth resistive heating molybdenum boat, and theresulting boats were fixed in the vacuum deposition apparatus.

After the pressure in the vacuum tank was reduced to 4×10⁻⁴ Pa, theabove heating boat carrying α-NPD was heated by applying an electriccurrent to evaporate α-NPD onto the transparent substrate at adeposition rate of 0.1 nm/sec to form a positive hole transport layer of40 nm in thickness. Further, the above heating boat carryingillustrative compound H-21 was heated by applying an electric current toevaporate illustrative compound H-21 onto the positive hole transportlayer at a deposition rate of 0.1 nm/sec to form an electron blockinglayer of 10 nm in thickness. Further, the above heating boats, eachcarrying CBP and illustrated compound 1-1, were heated by applying anelectric current to co-evaporate CBP and illustrated compound 1-1 ontothe above-described positive hole transport layer at a deposition rateof 0.2 nm/sec and 0.012 nm/sec respectively to form a light-emittinglayer of 40 nm in thickness. The temperature of the substrate duringdeposition was room temperature. Further, the above heating boatcarrying BCP was heated by applying an electric current to evaporate BCPonto the above-described light-emitting layer at a deposition rate of0.1 nm/sec to form an electron transport layer of 10 nm in thickness.The resulting electron transport layer also functioned as a holeblocking layer. Furthermore, the above heating boat carrying Alq₃ washeated by applying an electric current to evaporate Alq₃ onto theabove-described electron transport layer at a deposition rate of 0.1nm/sec to form an electron injection layer of 40 nm in thickness.Temperature of the substrate during deposition was room temperature.

Subsequently, a cathode was prepared by evaporating lithium fluoride andaluminum onto the above sample with 0.5 nm and 110 nm in thicknessrespectively, to prepare organic EL element 2-1.

Organic EL elements 2-2 to 2-45 were prepared in the same manner as inpreparation of organic EL element 2-1 except that CBP, which wasemployed as a host compound in a light-emitting layer, was changed tothose compounds given in Tables 4 and 5, illustrated compound 1-1, whichwas employed as a dopant compound in a light-emitting layer, was changedto those compounds given in Tables 4 and 5, and illustrated compoundH-21, which was employed in an electron blocking layer, was changed tothose compounds given in Tables 4 and 5.

Evaluations of Organic EL Elements 2-1 to 2-45

Similarly to Example 1, the prepared organic EL elements 2-1 to 2-45were evaluated, with the results shown in Tables 4 and 5.

External quantum efficiency and emission life given in Tables 4 and 5were expressed by a relative value based on the external quantumefficiency and emission life of organic EL element 1-1 being 100.

TABLE 4 Organic EL Electron Guest Compound Host Compound ExternalElement Blocking Com- HOMO LUMO Com- T1 Tg Quantum No. Layer pound (eV)(eV) pound (nm) (° C.) Efficiency Life Note 2-1 H-21 1-1 −4.37 −0.57 CBP465 109 111 99 Comp. 2-2 — 1-1 −4.37 −0.57 CBP 465 109 100 100 Comp. 2-3H-21 1-2 −4.53 −0.76 CBP 465 109 105 105 Comp. 2-4 H-21 1-5 −4.18 −0.42CBP 465 109 103 89 Comp. 2-5 — 1-2 −4.53 −0.76 CBP 465 109 98 115 Comp.2-6 H-21 1-1 −4.37 −0.57 H-1 411 64 170 120 Inv. 2-7 H-21 1-1 −4.37−0.57 H-20 437 92 165 146 Inv. 2-8 H-21 1-1 −4.37 −0.57 H-19 445 130 163168 Inv. 2-9 H-21 1-1 −4.37 −0.57 H-18 446 180 169 174 Inv. 2-10 H-211-1 −4.37 −0.57 H-21 449 80 171 122 Inv. 2-11 H-21 1-1 −4.37 −0.57 H-29449 142 172 146 Inv. 2-12 H-21 1-2 −4.53 −0.76 H-1 411 64 170 130 Inv.2-13 H-21 1-2 −4.53 −0.76 H-20 437 92 168 155 Inv. 2-14 H-21 1-2 −4.53−0.76 H-19 445 130 169 175 Inv. 2-15 H-21 1-2 −4.53 −0.76 H-18 446 180179 171 Inv. 2-16 H-21 1-2 −4.53 −0.76 H-21 449 80 169 128 Inv. 2-17H-21 1-2 −4.53 −0.76 H-29 449 142 167 160 Inv. 2-18 H-21 1-5 −4.18 −0.42H-19 445 130 167 110 Inv. 2-19 H-21 1-5 −4.18 −0.42 H-20 437 92 170 113Inv. 2-20 H-22 1-1 −4.37 −0.57 H-20 437 92 169 146 Inv. 2-21 H-22 1-1−4.37 −0.57 H-19 445 130 171 167 Inv. 2-22 H-22 1-1 −4.37 −0.57 H-18 446180 167 175 Inv. 2-23 H-22 1-2 −4.53 −0.76 H-20 437 92 165 155 Inv. 2-24H-22 1-2 −4.53 −0.76 H-19 445 130 160 175 Inv. 2-25 H-22 1-2 −4.53 −0.76H-18 446 180 173 171 Inv. 2-26 H-28 1-2 −4.53 −0.76 CBP 465 109 105 111Comp. 2-27 — FIrpic −5.99 −2.36 H-21 449 80 153 50 Comp. 2-28 H-21FIrpic −5.99 −2.36 H-1 411 64 150 52 Comp. T1: Phosphorescent 0-0 BandComp.: Comparative Example, Inv.: Present Invention

TABLE 5 Organic EL Electron Guest Compound Host Compound ExternalElement Blocking Com- HOMO LUMO Com- T1 Tg Quantum No. Layer pound (eV)(eV) pound (nm) (° C.) Efficiency Life Note 2-29 H-21 1-75 −4.34 −0.55H-32 437 166 170 188 Inv. 2-30 H-21 1-77 −4.36 −0.66 H-32 437 166 170180 Inv. 2-31 H-21 1-79 −4.26 −0.47 H-32 437 166 165 169 Inv. 2-32 H-211-75 −4.34 −0.55 H-36 416 169 168 194 Inv. 2-33 H-21 1-75 −4.34 −0.55H-37 443 143 164 184 Inv. 2-34 H-21 1-77 −4.36 −0.66 H-36 416 169 164185 Inv. 2-35 H-21 1-77 −4.36 −0.66 H-37 443 143 162 181 Inv. 2-36 H-211-79 −4.26 −0.47 H-36 416 169 169 190 Inv. 2-37 H-21 1-79 −4.26 −0.47H-37 443 143 166 182 Inv. 2-38 H-21 1-79 −4.26 −0.47 H-37 443 143 168159 Inv. 2-39 H-22 1-75 −4.34 −0.55 H-32 437 166 165 186 Inv. 2-40 H-221-75 −4.34 −0.55 H-36 416 169 164 192 Inv. 2-41 H-22 1-75 −4.34 −0.55H-37 443 143 166 177 Inv. 2-42 H-22 1-77 −4.36 −0.66 H-36 416 169 155186 Inv. 2-43 H-22 1-77 −4.36 −0.66 H-37 443 143 151 180 Inv. 2-44 H-221-79 −4.26 −0.47 H-36 416 169 161 187 Inv. 2-45 H-22 1-79 −4.26 −0.47H-37 443 143 162 174 Inv. T1: Phosphorescent 0-0 Band Inv.: PresentInvention

Tables 4 and 5 show that the organic EL elements of the presentinvention achieved high external quantum efficiency and long life.

Example 3 Production of Full-Color Display

(Preparation of Blue Light Emitting Element)

Organic EL element 1-14 prepared in Example 1 was employed as a bluelight emitting element for the full-color display.

(Preparation of Green Light Emitting Element)

A green light emitting element was prepared in the same manner as inorganic EL element 1-14 in Example 1 except that the host compound andthe dopant were changed to CBP and Ir-1 respectively, and the resultingelement was employed as a green light emitting element for thefull-color display.

(Preparation of Red Light Emitting Element)

A red light emitting element was prepared in the same manner as inorganic EL element 1-14 in Example 1 except that the host compound andthe dopant were changed to CBP and Ir-9 respectively, and the resultingelement was employed as a red light emitting element for the full-colordisplay.

The above prepared red, green, and blue light emitting organic ELelements were juxtaposed on the same substrate to prepare a full colordisplay apparatus driven by an active matrix method having the formillustrated in FIG. 1. In FIG. 2, a schematic drawing of only displaysection A of the above-described display apparatus is shown. Namely,provided on one substrate are, a wiring section containing a pluralityof scanning lines 5 and a plurality of data lines 6, and a plurality ofpixels 3 (pixels emitting red light, pixels emitting green light, andpixels emitting blue light) which were juxtaposed. Each of scanninglines 5 and data lines 6 on the wiring section is composed of anelectroconductive material. Scanning lines 5 and data lines 6 cross eachother at right angles in a grid like fashion, and both kinds of linesare connected to pixels 3 at the crossing points (the details are notillustrated). Each of the plurality of pixels 3 described above isdriven by an active matrix method in which an organic EL elementcorresponding to each light-emitting color, a switching transistor and adriving transistor both of which are active elements are provided. Whenscanning signals are applied through scanning line 5, each pixelreceives an image data signal through data line 6, whereby each pixelemits light based on the received image data. Thus the aforesaid lightemitting pixels of red, green, and blue are suitably juxtaposed on thesubstrate, to produce a full color display.

It was confirmed that driving the above-described full color display canprovides a distinct full color moving picture exhibiting highbrightness, and high durability.

Example 4 Production of White Light Emitting Element and White LightLighting Device

An electrode of the transparent electrode substrate of Example 1 wasformed by patterning, on which a layer of α-NPD of 40 nm in thicknesswas formed as a positive hole injection/transport layer similarly toExample 1. Then, each of illustrative compound H-19, illustrativecompound 1-2, and Ir-9 was placed on the above-described heating boats,and was independently evaporated onto the above layer, by applying anelectric current, to a total layer thickness of 30 nm, by controllingdeposition rates of illustrative light-emitting host compound H-19,illustrative light-emitting dopant 1-2, and Ir-9 to be 100:5:0.6, toprovide a light-emitting layer.

Subsequently, a positive hole blocking layer was provided by forming alayer of BCP exhibiting 10 nm in thickness. Further, an Alq₃ layerexhibiting 40 nm in thickness was formed, to provide an electrontransport layer.

Next, similarly to Example 1, a stainless-steel mask, having squareholes with almost the same shape as the transparent electrode, wasprovided on the electron injection layer, and then a lithium fluoridewas evaporated to form a layer as a cathode buffer layer with 0.5 nm inthickness, and aluminum was evaporated to form a layer as a cathode with150 nm in thickness.

Using the above element, a flat lamp, having a sealed structure of thesimilar structure and similar method to that of Example 1, was produced.The above flat lamp emitted a nearly white light by applying an electriccurrent to prove that the aforesaid lamp is usable as a lighting device.

What is claimed is:
 1. An organic electroluminescent element comprisinga substrate having thereon an electrode and at least one organic layer,wherein at least one of the organic layers is a light-emitting layercontaining a phosphorescent compound and a host compound, and thephosphorescent compound is represented by Formula (A),

wherein R₁ represents a substituent; Z represents a group of non-metalelements necessary to form a five- to seven-membered ring; n1 is aninteger of 0 to 5; B₂ represents a nitrogen atom, B₁ and B₃-B₅ eachrepresents a carbon atom, a nitrogen atom, an oxygen atom or a sulfuratom, at least one of B₁ and B₃-B₅ represents a nitrogen atom; M₁ is ametal of 8-10 group in the periodic table; X₁ and X₂ each represent acarbon atom, a nitrogen atom or an oxygen atom; L₁ is a group ofelements forming ligands having coordination number 2 with X₁ and X₂; m1is an integer of 1 to 3; m2 is an integer of 0 to 2; and m1+m2 is 2 or3, and the phosphorescent compound has a HOMO of from −5.15 to −3.50 eVand a LUMO of from −1.25 to +1.00 eV, and the host compound has a 0-0band of 460 nm or less in a phosphorescence spectrum and the hostcompound is represented by Formula (1),

wherein R_(1a) represents a hydrogen atom, an aliphatic group, anaromatic group, or a heterocyclic group; R₁ and R₂ each represent ahydrogen atom or a substituent; at least one of R₁ represents adibenzofuryl group; n1 is an integer of 1-4, and n2 is an integer of0-4; and wherein the host compound has a glass transition temperature of130° C. or more.
 2. The organic electroluminescent element of claim 1,wherein the phosphorescent compound has the HOMO of from −4.80 to −3.50eV and the LUMO of from −0.80 to +1.00 eV.
 3. The organicelectroluminescent element of claim 1, wherein m2 is 0 in thephosphorescent compound represented by Formula (A).
 4. The organicelectroluminescent element of claim 1, wherein Formula (A) is furtherrepresented by Formula (B),

wherein R₁, R₂ and R₃ each represent a substituent; Z represents a groupof non-metal elements necessary to form a five- to seven-membered ring;n1 is an integer of 0 to 5; M₁ is a metal of 8-10 group in the periodicseries; X₁ and X₂ each are a carbon atom, a nitrogen atom or an oxygenatom; L₁ is a group of elements forming ligands having coordinationnumber 2 with X₁ and X₂; m1 is an integer of 1 to 3; m2 is an integer of0 to 2; and m1+m2 is 2 or
 3. 5. The organic electroluminescent elementof claim 1, wherein the host compound is represented by Formula (2),

wherein R₁ and R₂ each represent a hydrogen atom or a substituent; atleast one of R₁ represents a dibenzofuryl group; n1 is an integer of1-4, and n2 is an integer of 0-4; R₃ represents a substituent; L₁represents a divalent linking group; and m1 is an integer of 0-5.
 6. Theorganic electroluminescent element of claim 1, wherein a glasstransition point of the host compound is 160° C. or more.
 7. The organicelectroluminescent element of claim 1, further comprising an electroninhibition layer.
 8. The organic electroluminescent element of claim 1,emitting white light.
 9. A display device comprising the organicelectroluminescent element of claim
 1. 10. An illuminating devicecomprising the organic electroluminescent element of claim 1.